Revert "[ADT] Fix some Clang-tidy modernize-use-using warnings; other minor fixes (NFC)."

This reverts commit r303383.

This breaks the modules-enabled macOS build with:

lib/Support/LockFileManager.cpp:86:7: error: declaration of 'gethostuuid' must be imported from module 'Darwin.POSIX.unistd' before it is required

llvm-svn: 303402